1. Field of the Invention
This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method for optimizing semiconductor processing.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the processing tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can engender nonoptimal control of critical processing parameters, such as throughput accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
Among the parameters it would be useful to monitor and control are the temperatures and lamp power levels that silicon wafers are exposed to during rapid thermal processing (RTP) used to activate dopant implants, for example. An RTP chamber heats up during successive wafer processing so that the thermal environment experienced by early wafers will be different from the thermal environment experienced by later wafers. For example, if the RTP chamber is not preheated, the first wafers will be run in a colder RTP chamber than later wafers. This will cause differences in wafer processing within a lot of wafers, leading to decreased satisfactory wafer throughput, decreased reliability, decreased precision and decreased accuracy in the semiconductor manufacturing process.
Sub-optimal preheating may also be problematic. For example, a manufacturer of rapid thermal annealing (RTA) tools provides a quartz tube temperature reading to the tool user to better understand the process conditions, and states that by preheating the tool (with a recipe similar to the production process recipe) to a set tube temperature, the tube temperature traces from the 1st workpiece can be made to overlap the tube temperature traces from the 2nd through 25th workpieces, and, thus the system is properly preheated. From experiments that have been conducted and the resulting experimental data, this preheat has been found to be insufficient and sub-optimal. The 1st workpiece received more of an anneal (a higher temperature) than the rest of the lot (a "1st workpiece effect"). This again caused differences in wafer processing within a lot of wafers, leading to decreased satisfactory wafer throughput, decreased reliability, decreased precision and decreased accuracy in the semiconductor manufacturing process.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.